Spectroscopic source unit



March 18, 1947. HASLER AL 2,417,489

SPECTRQSCOPIC vSOURCE UNIT Filed July 14, 1945 2 Sheet's-Shest l HIGHv0.1; 7216/; 10m TOR AND SYNCHRONOUS SWITCH INVENTORS. MAURICE F HASLERROLAND IV. LJNDHURS T Patented Mar. 18, 1947 SPECTROSCOPIC SOURCE UNITMaurice F. Hasler and Roland W. Lindhurst, Glendale, Calif.

Application July 14, 1943, Serial No. 494,754

19 Claims. 1

This invention relates generally to the art of spectrochemical analysis,and more particularly to spectroscopic source units. In spectrochemicalanalysis, an electric discharge between terminals at least one of whichconsists of the sample to be analyzed vaporizes a small portion of thesample and the resulting light exhibits the spectrum of the variouselements comprising the sample. The electric discharge has in someinstances been in the nature of an arc, either A. C. or D. C., givingthe characteristic arc spectrum, and in others has been in the nature ofa spark, giving a somewhat different spectrum in which certainsparklines are enhanced.

Before proceeding further, definitions of arcs and sparks appropriate tothe subject in hand should be attempted. An are may for spectrochemicalanalysis purposes be defined as that part of a discharge which startsabout one millisecond after an electrode gap has been broken down andcontinues for the duration of the discharge, provided the current is ofthe order of magnitude of amperes. The time, one millisecond, was chosenbecause it takes about that length of time for a discharge to achievethermal equilibrium. Before that time the discharge. is in a transitionstage that starts with a spark and gradually converts into an are. Thisis equally the case whether the discharge originates by applying asparking potential between the electrodes, as in the spark, or byelectrode contact, as usually employed in the D. C. arc. The current ofthe order of amperes assures that arcs suitable for spectrochemicalanalysis are being considered, arcs that allow the detection andmeasurement of elements at extremely small concentrations.

Definition of a spark is somewhat controversial and accordingly moredifficult. However, a spark may for present purposes be regardedgenerally as the initial breakdown of short duration of a gap under highvoltage. It may be oscillatory or heavily damped. As noted above, an arcmay be initiated by a spark, the first part of the discharge consistingof a spark which then converts into an arc.

An arc-type discharge results in relatively low electron velocities inthe gap, such that electron bombarded atoms of the vaporized elementsunder test have their electronic configurations modified, but do notlose electrons. The resulting spectrum is of a characteristic type, andthe discharge producing such a type is referred to as arc-like incharacter. A spark-type discharge produces high electron velocities,such as.

are capable of stripping one or more electrons of! the atom and excitingthe remaining atom to a high energy state by imparting energy to theremaining electronic structure. The resulting spectrum has othercharacteristic lines, and a discharge productive of such a spectrum isreferred to as being spark-like, irrespective of exact definition of theterm used.

Between discharges obtained from known socalled spark units and thoseobtained from true are sources is a relatively wide range of relativelyunexplored territory, and it is a general object 01' thepresentinvention to provide a source unit capable of exploring this territory.

Certain difficulties stand in the way of adjustment or conversion ofpresently known so-called spark units to produce discharges morearc-like in character. To illustrate, we may consider the conventionalhigh voltage alternating current spark unit in some detail. Such a unitusually consists of a high voltage transformer, providing from 10 to 40kilovolts in the secondary, a condenser that is charged once everyhalf-cycle by that voltage, and a discharge circuit connected across thecondenser and consisting of inductance, resistance and one or more sparkgaps in series. Such a circuit is self-igniting in that the power storedin the condenser is at a sufliciently high voltage to break down the gapor gaps at a certain time in the charging cycle. Oncethe gap is brokendown, the discharge proceeds independently of the charging circuit, andis dependent entirely upon the values of C, L and R, capacitance,inductance, and resistance, and upon the voltage E to which thecondenser was charged at the time of the breakdown. The current passingthrough the gap is, neglecting gap resistance,

11: Ec*L-* (e- (sin zL- cwhere i is the current and t is the time aftergap breakdown. The first term gives approximately the peak current forlow damping; the second term, the damping; while the third termrepresents the oscillations.

Assuming large E, C and R, say 40,000 volts 0.02 microfarad, and 15ohms, small L, a few microhenries, and a synchronous gap in series withthe analytical gap, a discharge will be obtained with a peak amperage ofabout 750 amperes, a duration of about 1.7 microseconds, giving threehalfeycles of about 0.6 microsecond per half-cycle. Such a discharge wespeak of as being very sparklike, irrespective of exact definition ofthe term used. it The spectrum obtained shows a. consider-.

able enhancement of spark lines over are lines for all elements detectedas compared to that obtained from an are for the same sample.

The spark characteristics of this discharge are due, first, to the highcurrent densities available which allow multiple electron-atomcollisions and thus excitation of atoms to very high energy states, andsecond, to the small concentration of. electrode atoms of low excitationpotential that prevail in the gap, because of the very short duration ofthe discharge. This small concentration of electrode atoms does notlimit the electron velocities by inelastic collisions with these atomsto the extent that large concentrations would, and thus everythingfavors the production of very spark-like spectra.

If this be considered as one of the mostsparklike cases obtainable withconventional apparatus, it is interesting to speculate upon whichmodifications might be introduced to make the discharge more arc-like.

In the theory of oscillating circuits, the formula given holds only forR /4L 1/LC. If

the circuit is critically damped and no oscillation occurs, while if R/4L 1/LC the circuit is overdamped and just as in the critically dampedcase, only a single pulse of current results. Thus, two directions ofchange are possible in the apparatus discussed previously that willmarkedly change the current vs. time characteristics. The first is theusual one employed where R/2L is made a great deal smaller by changing Rand L in the circuit. R can be reduced to little more than the gapresistance, which is of the order of magnitude of. an ohm, while Lcan beeasily increased to 1000 microhenries. This changes the damping termenormously, thus lengthening the total time of discharge; likewise themaximum current-to 180 amperes, and the time per half-cycle-to 14microseconds. If it were possible to charge the condenser to peakvoltage and then let it discharge without interruption, a total time ofdischarge app-roaching a millisecond would be obtained for these circuitconstants. Unfortunately the synchronous spark gap which must be used toallow the condensers to be charged to peak voltage, also limits the timeof discharge due to its strong quenchin action. Thus, though much morearc-like conditions can be obtained with a spark source unit under theseconditions than under those considered previously, are conditionssatisfying, our definition are not obtained.

The other direction of change is to make R. /4L large compared to l/LC.Since We have considered about as small an L as possible in our firstcase, this can only be accomplished by increasing R. Increasing R to 20ohms will provide a critically damped unidirectional spark. Byincreasing the resistance further, the maximum current would be droppedand the time of spark duration increased. The maximum time of dischargepossible turns out to be about 100 microseconds, utilizing a resistanceof ten thousand ohms. This gives a maximum current of a few amperes,which, over the short time available, provides only a small amount ofluminous energy in the gap. This modification of the spark thus does notallow the production of true arc-like spectra, though it represents atrend in that direction.

Thus, one is forced to the conclusion that the conventional constants ofthe high voltage spark unit with synchronous gap are not such as toallow the production of true arc-like spectra. In fact, they are suchthat they do not allow much study of even the transitionary stagesbetween spark breakdown of a gap and true are conditions.

The alternative is the modification or conversion of arc-type sourceunits to produce spectra more spark-like in character. The usual A. C.are employed in spectroscopic analysis has a duration of from four tosix milliseconds, and hence comes under the category of an are by ourdefinition. One approach of the present invention is to attempt theshortening of the duration of the A. C. are until it is of the order ofa millisecond or less.

Particular objects of the invention are the following:

To provide a source unit circuit capable of producing discharges bothoscillatory and unidirectional and capable of being varied from timedurations of much less than a millisecond (sparklike) to durations ofseveral milliseconds (arclike), to give a variety of excitationconditions ranging from spark to arc;

To provide a source unit circuit that charges a condenser to a definitepredetermined voltage prior to each gap breakdown, so as to assurereproducibility of the quantity of electricity available for eachdischarge; and

To provide a source unit circuit in which only the analytical gap is inthe discharge circuit, so that termination of the discharge will bedependent only on the discharge circuit and gap constants.

With this preliminary discussion in mind, the invention will now be bestunderstood by referring to the following detailed description of anillustrative embodiment thereof, reference being had to the accompanyingdrawings, in which:

Fig. 1 is a schematic wiring diagram of a source unit in accordance withthe invention;

Fig. 2 is a schematic wiring diagram of a modified source unit inaccordance with the invention;

Fig. 3 is a chart showing oscillograms of discharges obtained with thecircuits of Figs. 1 or 2 as resistance in the discharge circuit isvaried;

Fig. 4 shows oscillograms of the charge and discharge currents in thepower circuit when the discharge is initiated during the alternatehalfcycles from the charge;

Fig. 5 shows oscillograms of the charge and discharge currents when thedischarge is initiated during the charging period; and

Fig. 6 shows oscillograms of charge and discharge current with thedischarge initiated after the condensers are charged but before the nextcharging cycle so that the discharge may utilize that charging power.

In Fig. 1, showing one simple specific exemplification of the invention,the input circuit, adapted to be furnished with electric power fromcommercial alternating current power mains (low frequency, e. g., 50 or60 cycles), is designated at I0, and feeds electrical energy to theparallel connected primary windings of power and high voltagetransformers II and i2, respectively.

The secondary winding of transformer l2 feeds a high voltage ignitercomprising the circuit I 3, I4 connected across the electrodes formingthe analytical gap l5. In the specific form of Fig. 1 the circuit lead14 includes rectifier l6, resistor I1 and a synchronous gap or switchl8, while a capacitor I9 is connected between lead l3 and lead [4 at apoint between the rectifier and the resistor. The synchronous gap orswitch l6 may be of any conventional nature, and have anyconventionalarrangements whereby it will be closed in synchronous relation with thecommercial frequency power current from the mains It). It is hereconventionally indicated as controlled or driven through circuit leads2%] fed from mains l0.

The secondary winding of transformer H feeds the power circuit 22, 23across which is connected at variable condenser bank 24. A rectifier forthe circuit 22, 23 is shown as placed in the lead 22, as at 25, and lead22 is also shown as including an iron core inductance 21 serving as asurge suppressor.

A discharge circuit 30, 3|, forming a part or continuation of powercircuit 22, 23, and including a variable power resistor 32 and variableinductor 33, connects the condenser bank 24 across the analytical gapI5.

The above described circuit is merely one example of variouspossibilities within the scope of the invention; in particular, theignitor is subject to wide modification, the only general requirementbeing that a high voltage ignitor be connected to the analytical gap,and have incorporated therein a synchronous switch arranged to be closedin synchronous relation with the power current. The ignitor circuit maybe of various types, and the synchronous switch may also be of anydesired nature, such as a rotary synchronous gap, a synchronouselectronic switch triggered from the power circuit, etc., all as will beentirely evident to those skilled in the art. In fact, an auxiliary gapignitor of any type whatsoever may be used, so long as its operation issynchronized with the charging of the power condenser. I-lowever, we mayset forth typical con stants of one illustrative circuit (that ofFig. 1) which has been found to give satisfactory results. The secondaryvoltage of ignitor transformer 22 may have a peak voltage of 15,000volts, and the secondary of power transformer H, a peak voltage of theorder of 1,000 volts. Capacitor l9 may have a capacitance of .0025 mi.and resistor l9 may have a resistance of the order of 12 ohms. Variablecapacitor 24 has a capacitance range of 1 to 60 mi. in steps of one mf.Variable resistance 32 has a resistance range of 1 to 400 ohms in stepsof 1 ohm, and variable inductance 33 has a range of 25 to 400microhenries.

Operation of the circuit of Fig. 1 is as follows:

A half-wave rectified current flows from the secondary of transformer l2to charge the condenser l9 to a predetermined peak voltage. Thiscondenser being charged, and the synchronous gap til then closing, thecondenser then discharges across the gap l5 through the resistor ll. Itis to be understood that the synchronous gap i8 is closed once eachcycle, and the time of closure is adjusted to occur after the completionof the charging of the condenser [9. The synchronous gap is of courseopen by the time the next charging begins.

During the charging of the condenser l9 through rectifier 16 fromtransformer 12, the power condenser 24 is being charged to apredetermined peak voltage through the rectifier 25 from the powertransformer II. The presence of the rectifier 25 prevents the condenserfrom discharging through the circuit 22, 23, and the analytical gap I5is too wide for a discharge to take place thereacross under the voltageto which condenser 24 has been charged. Discharge of condenser 24 acrossgap I5 is accordingly deferred until the gap is fired by discharge fromcondenser 19, which occurs upon closure of synchronous gap I8 during thehalf-cycle succeeding the charging half-cycle. Upon such closure ofsynchronous gap I8, condenser I9 discharges across analytical gap l5,and said gap being broken down, power condenser 24 then dischargesthereacross, and the gap bein ionized, such discharge continues totermination, despite relatively short duration of the igniting dischargefrom condenser Fig. 4 shows, above, an oscillogram of the chargingcurrent of the condenser 24, and below, an oscillogram of the dischargecurrent from said condenser. Attention is directed to the fact that thecharging current drops to zero before the start of-the dischargingcurrent, indicating clearly their complete independence. As heretoforementioned, the point of initiation of the discharge is adjustable withthe synchronous gap in the ignitor circuit, and although this point canbe adjusted with great precision, it is of small significance so long asthe discharge starts after the charging has ceased, and ends before thenext charging begins. This is in contradistinction to the usualsynchronous gap adjustment wherein such adjustment determines the exactvoltage to which the condensers are charged.

Thus, breakdown of the gap is performed with the low powered ignitorcircuit, and the main dis charge then proceeds independently of theconstants of the ignitor circuit. This provides the great advantage ofallowing relatively long discharges, the duration of which depend onlyupon the power circuit and gap constants. An incidentalpracticaladvantage of the arrangement is that the synchronous gap only carriesthe low power of the ignitor circuit, and hence its sparking electrodeshave a very long life.

By utilizing the indicated relatively low Voltages in the power circuit,it is feasible to employ very high values of capacitance. This allowsoverdamped discharges to be employed which possess long time constantsand which pass large amounts of energy through the analytical gap. Thus,this type of discharge, which was impractical in the case of standardspark units due to the capacitance available, becomes a practical modeof operation.

It should be mentioned that in practice it has been found important forreproducibility of results that the capacitor [9 in the ignitor circuitof Fig. 1 be charged to an accurately predetermined voltage.

In Fig. 2 we have shown a modified coupling of the ignitor to theanalytical gap. In this instance we have shown the ignitor andsynchronous switch merely in block diagram, since the ignitor portion ofthe circuit as well as the synchronous switch are particularly subjectto variation, and many substitute arrangements will occur to thoseskilled in the art. The power portion of the circuit is essentially thesame as in Fig. l, and corresponding circuit elements are accordinglydesignated by like reference numerals, but with the numerals primed inthe case of Fig. 2. The two circuit leads ma from the input circuit IEto the ignitor and synchronous switch indicate conventionally thesynchronizing connection by which the synchronizing switch is closed inproper cyclical relation with the input current in the circuit W. Thedischarge circuit 30, 3| which connects the power condenser 24' acrossthe analytical gap l5 contains variablefresistor 32,, and variableinductor 33', and

it also includes, between the inductor 33 and the gap 15', the secondarywinding 40 of atransformer whose primary M is fed by the output of thesynchronously switched ignitor. The inductance of the winding 40 is madesmall relatively to that of inductor 33'. A high frequency by-zpasscondenser 42, of a capacity of the order of .'01 mf., is connected froma point between inductor 33 and winding 40 to the circuit lead $1 on theother side of the gap.

The operation of the circuit of Fig. 2 is essentially the same as thatof Fig. 1, with the exception of the manner in which the ignitingdischarge is conveyed from the ignitor to the gap. In the case of Fig.2, the oscillating discharge current in the output circuit of the*ignitor, initiated by closure of the normally open synchronous switch,sets up an oscillatory discharge current in the oscillating circuit madeup of winding 40, condenser '42., and the gap. The gap being thus brokendown, discharge of power condenser 24' thereacross proceeds as before.The circuit of Fig. 2 has the unique advantage, however, that no leakageoccurring between the two sides 3E! and 3| of the discharge circuit willadversely affect the igniting discharge voltage applied across the gap.As a matter of fact, any such leakage actually means greaterconductance, and hence enhanced applied voltage across the gap.

The circuit as thus described meets the objectives preliminarilyoutlined. The usual limitations in time constants associated with theconventional spark source are entirely eliminated. Fig. 3, above, showsoscillograms of oscillatory discharges of increasing damping anddecreasing duration as the series resistance of the discharge circuit isgradually increased. Fig. 3, below, shows critically dampened dischargesbeginning with a duration of the order of a millisecond and graduallyincreasing as the series resistance of the discharge circuit is furtherincreased. Arc-type spectra are obtained with the discharge representedby the upper oscillogram to the left and the spectra become increasinglyspark-like as series discharge circuit resistance is increased, becomingvery spark-like for the conditions represented by the last oscillogramabove and the first oscillogram below. The spectra gradually become morearc-like in character as the discharge circuit resistance is thenfurther increased .until the last oscillogram below is reached. Thefirst and last oscillograms thus represent arc-type dischargeconditions, giving arclike spectra; however, while these conditionsresemble one another insofar as the duration of discharge and thespectra produced are concerned, the oscillatory condition of the onecase and the critically dampened character of the other develop someuseful differences in the spectra. The two middle conditions representedcomprise a heavily damped spark-like oscillatory discharge, and acritically damped sparklike unidirectional discharge.

The series of oscillographs of Fig. 3 were obtained simply by increasingthe series resistance of the discharge circuit. A series ofrepresentative results can also be obtained by beginning with a highlydamped spark of short duration, and gradually increasing the inductanceand decreasing the resistance of the discharge circuit to obtain longerand longer oscillating discharge periods, and more and more arc-likespectra. Another series of results can be obtained by starting with thecritically damped case, and increasing the resistance to obtain longerand longer unidirectional discharge periods. These two lastmen-tionedstudies are, however, in effect telescoped into 'one another by theseries of tests represented in Fig. 3, in which merely the resistanceparameter is varied. The variable resistance and variable inductance canbe regarded as a variable resistor and inductor combination, in whicheither the resistor, or the inductor, or both, may be made variable tovary the type of discharge.

The phase of the ignitor circuit may be changed so that it causes adischarge to be initiated during the charging cycle of the powercircuit, giving the results represented in Fig. 5. In this case, thedischarge gap is broken down during the charging of the power condenser24, Whereupon said condenser discharges across the gap, and current fromthe power transformer II also discharges across the gap, continuinguntil the half-cycle is ended. The duration of the discharge may thus becontrolled by varying the time of initiation, and the discharge is inthe nature of an interrupted D. C. are.

Fig. 6 shows another alternative mode of operation of the unit,involving a combination of the overdamped discharge and the dischargerepresented in Fig. 5. The power condenser 24 is charged during thefirst half-cycle. During the next half-cycle preferably immediatelypreceding the next following half-cycle, the synchronous gap closes andthe ignitor circuit breaks down the analytical gap, so that the chargedpower condenser discharges thereacross. This discharge continues intothe next charge period which adds a power discharge derived from thepower transformer. The discharge is thus in the nature of a condenserdischarge followed by a rectified power discharge. The discharge occursonly on alternate cycles, since the power condenser is empty on theother alternate cycles and is hence (assuming 60 cycle power) of a 30cycle frequency, and is of very long duration, up to sixteenmilliseconds.

The system thus provides for the obtainment of a wide variation inspectra, and permits exploration through the entire region fromoscillatory are conditions through oscillatory and critically dampenedspark conditions to critically damped arc conditions.

For a discussion of the appearance of the spectra of discharges that areintermediate the arc and the spark, as obtained with the new source unitof the present invention, see A new spectroscopic source unit, by M. F.Hasler and H. W. Dietert, Journal of the Optical Society of America, Api 1943, vol. 33, No. 4, pp. 218228.

We claim:

1. In a spectroscopic source unit, the combination of an analytical gapconsisting of two spaced electrodes, 2. power circuit connected acrosssaid two gap electrodes, a power condenser in said power circuit adaptedand arranged to be charged by current supplied to said power circuit andto discharge across said gap upon ignition of the latter, a lowfrequency source of unidirectional condenser-charging current impulsesfor said power circuit, a high voltage ignitor circuit conductivelyconnected across said two gap electrodes and adapted to initiatedischarge thereacross, and a synchronous switch adapted to periodicallyclose said ignitor circuit in a synchronous relation with the lowfrequency current impulses supplied by said source.

2. In a spectroscopic source unit or the like, the combination of:two'spaced electrodes forming an analytical gap, a power circuitconnected across said two gap electrodes, a power condenser across saidpower circuit ararnged to be charged means in said power circuit betweensaid source and said power condenser causing said power condenser to becharged unidirectionally and only on alternate half-cycles, an ignitorembodying a discharge circuit adapted and arranged to peri odicallysupply a breakdown voltage to said gap, and a, synchronous switchcontrolling the discharge of said ignitor in a synchronous relationshipwith the low frequency current supplied by said alternating currentpower source.

3. In a spectroscopic source unit or the like, the combination of: twospaced electrodes forming an analytical gap, a power circuit connectedacross said two gap electrodes, a power condenser in said'power circuitarranged to be charged by current impulses flowing in said power circuitand to discharge across said gap upon ignition of the latter, a resistorand an inductor in series circuit between said power condenser and saidanalytical gap, a low frequency alternating current power source forsaid power circuit, said source being of a voltage incapable of breakingdown said gap via said power circuit, half-wave rectifier means in saidpower circuit between said source and said power condenser causing saidpower condenser to be charged unidirectionally and only on alternatehalf cycles, an ignitor embodying a discharge circuit, adapted andarranged to periodically supply a breakdown voltage to said gap, and asynchronous switch controlling the discharge of said ignitor in asynchronous relationship with the low frequency current supplied by saidalternating power source.

4. In a, spectroscopic source unit, the combination of: two spacedelectrodes forming an analytical gap, a high voltage ignitor circuitconnected across said two gap electrodes, a condenser across saidignitor circuit adapted to discharge across said gap, a power circuitconnected across said two gap electrodes in parallel with said ignitorcircuit, a power condenser connected across said power circuit, avariable resistor and a variable inductance in circuit between saidpower circuit and said analytical gap, a resistor and a synchronous gapin circuit between said ignitor circuit condenser and said analyticalgap, and means for energizing said ignitor andpower circuits withpulsating unidirectional currents to charge said condensers, saidsynchronous gap being timed to close following charging of said ignitorcircuit condenser.

5. In a spectroscopic source unit, the combination of: twospacedelectrodes forming an analytical gap, a high voltage ignitorcircuit connected across said two gap electrodes, a condenser acrosssaid ignitor circuit adapted to discharge across said gap, a powercircuit connected across said two gap electrodes in parallel with saidignitor circuit, a power condenser connected across said power circuit,a variable resistor and a variable inductance in circuit between saidpower circuit and said analytical gap, a resistor and a synchronous gapin circuit between said ignitor circuit condenser andsaid analyticalgap, and

means for energizing said ignitor and power circuits with half-waverectified alternating currents to charge said condensers, saidsynchronous gap being timed to close following charging of said ignitorcircuit condenser.

6. In a spectroscopic source unit, the combination of: two spacedelectrodes forming an analytical gap, a high voltage ignitor circuitconnected across said two gap electrodes, a condenser across saidignitor circuit adapted to discharge across said gap, at power circuitconnected across said two gap electrodes in parallel with said ignitorcircuit, a power condenser connected across said power circuit, avariable resistor and a variable inductance in circuit between saidpower circuit and said analytical gap, a resistor and a synchronous gapin circuit between said ignitor circuit condenser and said analyticalgap, and means for energizing said ignitor and power circuits within-phase half-wave rectified alternating currents to charge saidcondensers, said synchronous gap being timed to'close following charg:ing of said ignitor circuit condenser. g

7. In a spectroscopic sourceunit, the combination of: an analytical gap,a high-voltage ignitor circuit connected across said two gap electrodes,a condenser across said ignitor circuit adapted to discharge across saidgap, a power circuit con--; nected across said two gap electrodes inparallel with said ignitor circuit, a power condenser connected acrosssaid power circuit, a variable resistor and a variable inductance incircuit between said ignitor circuit condenser and said analytical gap,and means for energizingsaid ignitor and power circuits with 180out-of-phase half-wave rectified alternating currents to charge saidcondensers, said synchronous gap being timed to close following chargingof said ignitor circuit condenser.

8. In a spectroscopic source unit, the combina tion of: two spacedelectrodes forming an analytical gap, at high voltage ignitor circuitconnected across said two gap electrodes, a condenser across saidignitor circuit adapted to, discharge across said gap, 2, power circuitconnected across said two gap electrodes in parallelwith said ignitorcircuit, a power condenser connected across said power circuit, avariable resistor and a variable inductance in said power circuitbetween said power condenser and said analytical gap, a resistor and asynchronous gap in said ignitor circuit between said ignitor circuitcondenser and said analytical gap, a source of alternating currentpower, means fed from said source of power for impressing a relativelyhigh voltage across said ignitor circuit, a half-wave rectifier in saidignitor circuit ahead of said'ignitor circuit condenser, means fed fromsaid source of power for impressing a voltage across said power circuit,and a half-wave rectifier in said power circuit ahead of said powercircuit condenser, said-synchronous gap being timed to close followingchargingof said ignitor circuit condenser through said rectifienwherebysaid condenser discharges across said analytical gap to thereby permitsaid power circuit condenser to discharge across said analytical gap.

9. In a spectroscopic source unit, thecombination of two spacedelectrodes forming an analytical gap, a power circuit, a power condenserconnected across said power circuit, a low frequency alternating currentpower source for said power circuit, said source being of a voltageincapable of breaking down said gap via said power circuit, ha t-waverectifier means in said power circuit causing said power condenser to becharged. onalternate half. cycles; a discharge. circuit forming acontinuation of said power' circuit connecting said power condenseracross said two gap electrodes, a variable resistor and. inductorcombination in series in said discharge circuit, aby-pass condenserconnected across said discharge condenser on the gap side of saidresistor and inductor combination, and a synchronous high voltage. gapignitor having an output circuit inductivity coupled to said dischargecircuit at a point between said by-pass condenser and one. of said gapelectrodes.

In a spectroscopic sourcev unit or the like, the combination of: twospaced electrodes forming an analytical gap, a power circuit connectedacross said two gap electrodes, a power condenser across said powercircuit arranged to be. charged by current impulses flowing in saidpower circuit and to discharge across: said gap upon ignition of thelatter, a low frequency'alternating current power source for said powercircuit, said source being of a voltage incapable of breaking down saidgapvia said power circuit, half-wave rectifier means in said powercircuit between said source and said power condenser causing said powercondenser to be charged unidirectionally and only on alternatehalf-cycles, and an. auxiliary ignitor for said gap operatedsynchronously with said alternating current su plied by said alternatingcurrent power source to periodically ignite said gap and therebyinitiatepower discharge thereacross.

11. In a spectroscopic source unit or the like, the combination of twospaced electrodes. forming an analytical gap, a power; circuitconnectedacross said two gap. electrodes, a power condenser across saidpower circuit arranged to be charged by current impulses flowing in saidpower circuit and to d scharge across said gap upon ignition of thelatter, a low frequency alternatingcurrent power source for said powercircuit, said source being of a voltage incapable of breaking down saidgap via said power circuit, half-wave. rectifier means in said power crcuit between said source and said power condenser causing said powercondenser to be charged unidirectionally and only on alternatehalf-cycles, and. an. auxiliary ignitor for said gap operatedsynchronously with said alternating current supplied by saidalternatingv current power source. to ignite said gap. each time. saidpower condenser is charged by a power current impulse in. said powercircuit and thereby initiate power discharge. there across.

12. In. a spectroscopic source unit or the. like, the combination of twospaced electrodes. forming an analytical gap, a power circuit connected.acrosssaid two gap electrodes, at power condenser across said powercircuit by current impulses flowing in said power circuit and todischarge across said gap upon ignition of the latter, a lowfrequencyalternating current power'source for said power circuit, saidsource being of avoltage incapable of breaking down said gap via saidpower circuit, half-wave rectifier means in said power circuit betweensaid source andsaid power condenser causing said power condenser to becharged unidirectionally and only on alternate half-cycles, and anauxiliary ignitor for said gap operated synchronously with saidalternating current supplied. by said alternating current power source.to ignite said gap following the termination of each complete chargingof said power condenser by a power current imarranged to be charged a 12pulse in said; power circuit and thereby initiate power discharge acrosssaid gap.

13. In a spectroscopic source unit or the like, the combination of twospaced electrodes form ing an analytical gap, a power circuit connectedacross said two gap electrodes, a power condenser across said powercircuit arranged to be charged by current impluses flowing in said powercircuit and. to discharge across said gap upon ignition of the latter, alow frequency alternating current power source for said power circuit,said source being of a voltage incapable of breaking down said gap viasaid power circuit, half-wave rectifier means in said power circuitbetween said source and said power condenser causing said powercondenser to be charged unidirectionally and only on alternatehalf-cycles, and an auxiliary ignitor for said gap operatedsynchronously with said alternating current supplied by said alternatingcurrent power source and adjusted to ignite said gap immediatelypreceding the said alternate condenser charging half-cycles and therebyinitiate power discharge thereacross.

14. In a spectroscopic source unit or the like, the combination of twospaced electrodes forming an analytical gap, a power circuit connectedacross said two gap electrodes, a power condenser across said powercircuit arranged to be charged by current impluses flowing in said powercircuit and to discharge across said gap upon ignition of the latter, avariable resistor and inductor combination in said power circuit betweensaid condenser and said gap, a low frequency alternating current powersource for said po er circuit, said source being of a voltage incapableof breaking down said gap via said power circuit. half-wave rectifiermeans in said power circuit between said sourcev and said powercondenser causing said condenser to be charged unidirectionally and onlyon alternate half-cycles, and an auxiliary ignitor for said gap operatedsynchronously with said alternating current supplied bv said alternatingcurrent power source to periodically ignite said gap and therebyinitiate power discharge thereacross.

15. In a spectroscopic source unit or the like, the. combination of: twospaced electrodes forming an analytical gap, a power circuit connectedacross said two gap electrodes, a power condenser across said powercircu t arranged to be charged by current impulses flowing in said powercircuit and to discharge across said gap upon ign tion of the latter, avariable resistor and inductor combination in sa d power circuit betweensaid condenser and said gap, a low ireouency alte nating current powersource for said po er circuit. said source being of a voltage incapableof breaking down said gap via said power circuit. half-wave rectifiermeans in said power circuit between said source and said power condensercausing said condenser to be charged unid rectional y and only onalternate half-cycles, and an aux liarv ignitor for said gap operatedsynchronou ly with said alternating current supplied by said alternatingcurrent power source to ignite said gap each t me said power condenseris charged bv a power current impulse in said power circuit and therebyinitiate power condenser discharge thereacross.

16. In a spectroscopic source unit or the like, the combination of: twospaced electrodes forming an analytical gap, a power circuit connectedacross said two gap electrodes, a power condenser across said powercircuit arranged to be charged by current impulses flowing in said powercircuit and to discharge across said cap upon ignition of the latter, avariable resistor and inductor combination in said power circuit betweensaid condenser and said gap, power means for establishing periodicunidirectional condenser-charging current impulses in said powercircuit, said power means operating at insufiicient voltage to breakdownsaid gap via said power circuit, and an auxiliary gap ignitor.synchronized with the flow of said periodic condenser-charging currentimpulses to ignite said gap and thereby initiate power condenserdischarge thereacross.

17. In a spectroscopic source unit, the combination of: two spacedelectrodes forming an analytical gap, a power circuit connected acrosssaid two gap electrodes, a power condenser in said pow er circuitadapted and arranged to be charged by current supplied to said powercircuit and to discharge across said gap upon ignition of the latter, alow frequency source of unidirectional condenser-charging currentimpulses connected to said power circuit, a high voltage ignitor adaptedand arranged to supply a breakdown voltage across said two gapelectrodes, and a synchronous switch adapted to periodically operatesaid ignitor in a synchronous relation with the low frequency currentimpulses supplied by said source.

18. In a spectroscopic source unit or the like, the combination of apower circuit, a power condenser connected in parallel thereacross, apair of spaced electrodes forming an analytical gap connected acrosssaid power circuit in parallel with said power condenser, a resistor andinductor combination in series in said power circuit between saidcondenser and said gap, an electric power source of low voltageconnected to said power circuit and adapted to create periodic condensercharging current impulses in said power circuit, the voltage of saidsource being insurficient to charge said condenser to a voltage capableof breaking down said gap, and an auxiliary gap ignitor synchronouslyoperated with said condenser charging current impulses to periodicallyignite said gap in step with charging of said condenser and therebyiintiate condenser discharges across said. gap.

19. In a spectroscopic source unit or the like, the combination of apower circuit, a power condenser connected in parallel thereacross, apair of spaced electrodes forming an analytical gap connected acrosssaid power circuit in parallel with said power condenser, a resistor andinductor combination in series in said power circuit between saidcondenser and said gap, an electric power source of low voltageconnected to said power circuit and adapted to create periodic condensercharging current impulses in said power circuit, the voltage of saidsource being insufflcient to charge said condenser to a voltage capabioof breaking down said gap, and an auxiliary gap ignitor embodying a highvoltage discharge circuit arranged to discharge across said gap andincluding synchronous switching means synchronized with said condensercharging current impulses to create a breakdown voltage across said gapfollowing each charging of said power condenser.

MAURICE F. I-IASLER. ROLAND W. LINDHURST.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number 7 Name Date 2,212,950 Pfeilsticker Aug. 27,1940 2,074,930 Marx Mar. 23, 1937 2,300,101 Capita Oct. 2'7, 1942

